Chloroplast biogenesis in plants is dependent upon the coordinated activities of two independent genetic systems localized in the chloroplast and the nucleus (see Cline and Henry (1996), Annu. Rev. Cell Dev. Biol. 12, 1-26). The vast constituent chloroplast proteins are encoded by the nuclear genes and are synthesized cytoplasmically- as precursor forms which contain N-terminal extensions known as transit peptides. The transit peptide is instrumental for specific recognition of the chloroplast surface and in mediating the post-translational translocation of pre-proteins across the chloroplast envelope and thence to the various different subcompartments within the chloroplast (e.g. stroma, thylakoid and thylakoid membrane).
Genes reported to have naturally encoded transit peptide sequences at their N-terminus include the chloroplast small subunit of ribulose-1,5-bisphosphate carboxylase (RuBisCo), de Castro Silva Filho et al. (1996) Plant Mol. Biol. 30: 769- 780; Schnell, D. J. et al. (1991) J. Biol. Chem. 266 (5): 3335-3342; 5-(enolpyruvyl) shikimate-3-phosphate synthase (EPSPS), Archer et al. (1990) J. Bioenerg. and Biomemb. 22 (6):789-810; tryptophan synthase. Zhao, J. et al. (1995) J. Biol. Chem. 2 70 (11):6081-6087; plastocyanin, Lawrence et al. (1997) J. Biol. Chem. 272 (33):20357-20363; chorismate synthase, Schmidt et al. (1993) J. Biol. Chem. 268 (36):27477-27457; and the light harvesting chlorophyll a/b binding protein (LHBP), Lamppa et al. (1988) J. Biol. Chem. 263: 14996-14999, although not all of these sequences have been useful in the heterologous expression of chloroplast-targeted proteins in higher plants.